Add a canvas object with drawRect() and inval().

experimental/SkV8Example/SkV8Example.h

 /*
  * Copyright 2013 Google Inc.
  *
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  */
 
 #ifndef SkV8Example_DEFINED
 #define SkV8Example_DEFINED
 
 #include <v8.h>
 
 #include "SkWindow.h"
 
-
 using namespace v8;
 
-
 class SkCanvas;
-
+class JsCanvas;
 
 class SkV8ExampleWindow : public SkOSWindow {
 public:
-   SkV8ExampleWindow(void* hwnd,
-                     Isolate* isolate,
-                     Handle<Context> context,
-                     Handle<Script> script);
-
+    SkV8ExampleWindow(void* hwnd, JsCanvas* canvas);
 
 protected:
     virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE;
 
-
-
 #ifdef SK_BUILD_FOR_WIN
     virtual void onHandleInval(const SkIRect&) SK_OVERRIDE;
 #endif
 
 private:
     typedef SkOSWindow INHERITED;
+    SkScalar fRotationAngle;
+    JsCanvas* fJsCanvas;
+};
+
+
+// Provides the canvas implementation in JS, and the OnDraw() method in C++
+// that's used to bridge from C++ to JS. Should be used in JS as:
+//
+//  function onDraw(canvas) {
+//   canvas.drawRect();
+//   canvas.inval();
+//  }
+//
+class JsCanvas {
+public:
+    JsCanvas(Isolate* isolate)
+            : fIsolate(isolate)
+            , fCanvas(NULL)
+            , fWindow(NULL)
+    {}
+    ~JsCanvas();
+
+    // Parse the script.
+    bool initialize(const char script[]);
+
+    // Call this with the SkCanvas you want onDraw to draw on.
+    void onDraw(SkCanvas* canvas, SkOSWindow* window);
+
+private:
+    // Implementation of the canvas.drawRect() JS function.
+    static void drawRect(const v8::FunctionCallbackInfo<Value>& args);
+
+    // Implementation of the canvas.inval() JS function.
+    static void inval(const v8::FunctionCallbackInfo<Value>& args);
+
+    // Get the pointer out of obj.
+    static JsCanvas* unwrap(Handle<Object> obj);
+
+    // Create a template for JS object associated with JsCanvas, called lazily
+    // by Wrap() and the results are stored in fCanvasTemplate;
+    Handle<ObjectTemplate> makeCanvasTemplate();
+
+    // Wrap the 'this' pointer into an Object. Can be retrieved via Unwrap.
+    Handle<Object> wrap();
+
     Isolate* fIsolate;
+
+    // Only valid when inside OnDraw().
+    SkCanvas* fCanvas;
+
+    // Only valid when inside OnDraw().
+    SkOSWindow* fWindow;
+
+    // The context that the script will be parsed into.
     Persistent<Context> fContext;
-    Persistent<Script> fScript;
-    SkScalar fRotationAngle;
+
+    // A handle to the onDraw function defined in the script.
+    Persistent<Function> fOnDraw;
+
+    // The template for what a canvas object looks like. The canvas object is
+    // what's passed into the JS onDraw() function.
+    static Persistent<ObjectTemplate> fCanvasTemplate;
 };
 
 #endif